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Coating with controlled grain size and morphology for enhanced wear resistance and toughness

a technology of grain size and morphology, applied in the direction of coatings, chemical vapor deposition coatings, coatings, etc., can solve the problems of increased toughness of coatings, difficult modification of conventional process adjustments, and inability to meet the requirements of hard and brittle materials with limited plasticity, etc., to achieve the effect of enhancing performance and wear resistan

Inactive Publication Date: 2007-08-16
SECO TOOLS AB
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0012] It is further an object of this invention to provide a coating layer of controlled grain size and morphology just above the nanograined region. According to this invention equiaxed grain morphologies with reduced grain sizes can be obtained in a controlled way. These coatings can be used in applications demanding high toughness and edge strength.
[0015] The above mentioned coatings can be used in combination with other CVD materials such as alumina to enhance the performance and wear resistance of the prior-art products.

Problems solved by technology

The MTCVD coatings are, however, very difficult to modify by conventional process adjustments.
This relation is, however, not necessarily correct for hard and brittle materials with limited plasticity.
The CO-doped nanograined MTCVD coatings exhibited increased toughness, however, with reduced crater wear resistance as a consequence.

Method used

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  • Coating with controlled grain size and morphology for enhanced wear resistance and toughness
  • Coating with controlled grain size and morphology for enhanced wear resistance and toughness
  • Coating with controlled grain size and morphology for enhanced wear resistance and toughness

Examples

Experimental program
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Effect test

example 1

[0043] This example demonstrates the effect of CO doping. CO doping was applied to obtain columnar and equiaxed structures with reduced and controlled grain sizes. The following four experimental coatings (referred to as coatings 1, 2, 3 and 4 ) were produced at a pressure of 70 mbar and at a temperature of 880° C. according to the process data given in Table 2. Compared with the U.S. Pat. No. 6,472,060, considerably lower amounts of doping were used except coating 4, which was produced according to prior art (U.S. Pat. No. 6,472,060). Coating 2 is deposited at a CO level of 0.8% and is composed of fine-grained columnar crystals. Coating 3 was deposited at CO doping level of 2.5% and is composed of equiaxed grains. In order to obtain equiaxed grain morphology above the nanograined region CO doping in the range of from about 2.0 to about 4.0%, preferably from about 2 to about 3% of the total gas flow can be used. The CO addition had to be controlled carefully so that the nanograined ...

example 2

[0044] The coatings were investigated using Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) in order to elucidate the effect of CO doping on the grain size and morphology. It appeared clear even in SEM that the microstructure of the typical MTCVD Ti(C,N) coating being composed of large columnar crystals (FIG. 1) can be refined by CO doping. The equiaxed grain morphology was obtained at CO doping level of from about 2.5% (FIG. 2). TEM revealed that at this CO level the grain size was not brought into the nanograined region and was about 60 nm. The grain size of Coating 4 deposited according to prior-art was in the nanograined region. The results are summarized in Table 3.

TABLE 3Grain size*)MorphologyCoating 11500 × 4000nmLarge columnarCoating 290 × 650nmNeedle-likeCoating 360nmSmall-equiaxedCoating 414nmNanograined

example 3

[0045] This example demonstrates the deposition of equiaxed grain morphology with controlled grain sizes. The effects of ZrCl4 and AlCl3 on the grain size and morphology with and without CO / CO2 doping are demonstrated.

TABLE 4H2N2CH3CNTiCl4ZrCl4(1 / min)(1 / min)(1 / min)(l / min)(%)AlCl3(%)CO2(%)CO(%)Coating 5balance45.50.552.12.50.00.00.0Coating 6balance45.50.552.10.70.00.02.1Coating 7balance45.50.552.10.01.50.03.0Coating 8balance45.50.552.10.03.00.23.0Coating 9balance45.50.552.12.50.00.23.0Coating 10balance45.50.552.12.53.00.23.0

[0046] The structure of coating 5 is shown in FIG. 3. The first part (about 2 um) was deposited without ZrCl4 doping. As very clear from the FIG. 4 the addition of 2.5% of ZrCl4 changed the coating morphology from columnar to equiaxed one (arrowed). Lower additions of ZrCl4 are needed to obtain the same structure as in Coating 5, if ZrCl4 is applied simultaneously with CO (coating 6). The same type of behavior could be obtained by adding AlCl3 together with CO (...

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Abstract

Wear resistance of the prior-art Ti(C,N) layers can be considerably enhanced by optimising the grain size and microstructure. This invention describes a method to obtain controlled, fine, equiaxed grain morphology in Ti(C,N) layers produced using moderate temperature CVD (MTCVD). The control of the grain size and shape can be obtained by doping using CO, CO2, ZrCl4 and AlCl3 or combinations of these. Doping has to be controlled carefully in order to avoid nanograined structures and oxidisation. This kind of coatings shows new enhanced wear properties. The fine grain size together with equiaxed grain morphology enhances the toughness of the coating with at least maintained wear resistance, which can be seen especially in sticky steels like stainless steels. The optimum grain size is from 50 to about 300 nm, preferably from about 50 to about 150. The coatings according to this invention are characterised by the lack of any strong preferred growth orientation, the length-to-width ratio (L / W) around 1 and only with a slight to moderate XRD line broadening.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to a cutting tool inserts consisting of a substrate at least partially coated with a coating consisting of one or more refractory layers of which at least one layer is a MTCVD-Ti(C,N)-layer composed of grains with grain size just above the nanograined region with equiaxed grain morphology. As a result the problem with grain boundary sliding at higher temperatures has been reduced and, consequently, wear resistance increased with almost maintained toughness. The inserts are particularly useful in applications where toughness is important, like in milling of adhering sticky stainless steels. [0002] Coated bodies used for metal cutting are well known. Typically, the bodies are made of a cemented carbide, cermet or ceramic and the coatings are one or more of a Group VIB metal carbide, nitride, oxide or mixtures thereof. For example, bodies of cemented carbides coated with layers of TiC, Ti(C,N), Al2O3 and TiN are widely us...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C23C16/14C23C16/30C23C16/36C23C30/00
CPCC23C16/36C23C30/005Y10T428/264Y10T428/256Y10T428/265Y10T428/252Y10T428/24355E04H1/125
Inventor RUPPI, SAKARI
Owner SECO TOOLS AB
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